1. Field of the Invention
The present invention relates to an exhaust control system for a motorcycle which is capable of controlling the flow rate of an exhaust gas.
2. Description of Background Art
An exhaust control system for a motorcycle in which a valve is provided in an exhaust passage in an engine exhaust system and the flow rate of an exhaust gas flowing through the exhaust passage is controlled by the valve has been put to practical use.
In the exhaust control system for a motorcycle in practical use, it has sufficient that the valve is provided in an exhaust pipe provided as the exhaust passage and the valve is opened and closed.
Such an exhaust control system for a motorcycle, wherein a connection pipe for connecting a muffler to an exhaust pipe is provided therein with an exhaust valve has been known. See, for example, Japanese Patent Laid-open No. 2002-138828.
FIG. 19 of the present drawings is a copy of FIG. 4 of Japanese Patent Laid-open No. 2002-138828. In FIG. 19, the same symbols as in Japanese Patent Laid-open No. 2002-138828 are used.
The exhaust control system for a motorcycle in Japanese Patent Laid-open No. 2002-138828 has a structure in which a multi-cylinder engine 16 is mounted on a vehicle body frame 2 with exhaust pipes 20 . . . (“ . . . ” means a plurality here and hereinafter) extending from individual cylinders of the engine 16. Some exhaust pipes 20, 20 are collected to a first collecting pipe (not shown) with a right coupling pipe 31 extending from the first collecting pipe. Other exhaust pipes 20, 20 are collected to a second collecting pipe 30 with a left coupling pipe 32 extending from the second collecting pipe 30. The left and right coupling pipe 32, 31 are collected to a third collecting pipe 33 with a connection pipe 22 being connected to the third coupling pipe 33. A muffler 21 is connected to the connection pipe 22 and the connection pipe 22 is provided therein with a vale mechanism 39 for controlling the flow rate of an exhaust gas.
A drive cable 40 extends from the valve mechanism 39. The drive cable 40 extends through the surrounding of a pivot shaft 13 of a swing arm 14 and a drive motor 41 is provided at the tip end of the drive cable 40. A CPU (central processor unit) 42 is provided for controlling the drive motor 41.
However, the exhaust control system for a motorcycle described in Japanese Patent Laid-open No. 2002-138828 has a problem in view of the fact that the drive cable 40 extends from the valve mechanism 39 and extends through the surrounding of the pivot shaft 13 of the swing arm 14. The drive cable 40 (hereinafter referred to as “the operating cable”) may possibly interfere with movable portions such as the swing arm 14.
In addition, in the exhaust control system for a motorcycle according to Japanese Patent Laid-open No. 2002-138828, the drive motor 41 (hereinafter referred to as “the servo motor”) is disposed on the rear side of the engine 16. Therefore, there is a demerit in that thermal influences of the engine 16 are exerted on the drive motor 41 and the CPU (central processor unit) 42 (hereinafter referred to as “the control unit”). Further, it may be desired to take into account the effective utilization of free spaces.
Further, in the exhaust control system for a motorcycle described in Japanese Patent Laid-open No. 2002-138828, a portion of the valve mechanism 39 projects toward the center of the vehicle body. Therefore, it is necessary to obviate the interference of the valve mechanism 39 with the vehicle body or component parts mounted on the vehicle. For example, there has been a problem wherein the connection pipe 22 has been moved outwardly in the vehicle width direction for obviating an interference with the valve mechanism 39 (hereinafter referred to as “the exhaust valve”) with the vehicle body side. As a result, the vehicle width is enlarged.
Still further, an exhaust control system for motorcycle wherein a valve mechanism is covered with a cover or cowling 23 is known. The valve mechanism is covered with a cowling 23. See, for example, Japanese Patent Laid-open No. 2002-138828.
The exhaust control system for a motorcycle described in Japanese Patent Laid-open No. 2002-138828, has a problem wherein the valve mechanism 39 is covered with the cowling 23 and the valve mechanism 39 (hereinafter referred to as “the exhaust valve”) is disposed at a position too far to cover with the cowling 23. Thus, it is necessary to use a new component part or parts, which increases the number of component parts.
In the case of covering the exhaust valve with a cover or the like, it is desired to cover the exhaust valve without increasing the number of component parts, by diverting the existing component parts as much as possible.